The Twombly Motor Company built a 7-cylinder rotary engine around 1912, giving 50 HP.

The pistons were 4 inches in bore and 4.5 inches in stroke.

The engine had steel cylinders and was equipped with Kingston carburetors and Bosch magnetos. The engine diameter was 36 inches.

From Appendix 10: In the American Aeronautics magazine for the month of May-June 1912, this engine brand, "Twombly Motor Co." appears installed on a model similar to the Bleriot and with identical landing gear.